DTC P0641: 5-Volt Reference Circuit Out Of Range: Description

WARNING: This page is about a different car, the 2003 GMC Envoy XL and 2003 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.

The Powertrain Control Module (PCM) provides 5 volts to the following sensors:

The Engine Oil Pressure (EOP) sensor.
The Manifold Absolute Pressure (MAP) sensor.
The engine cooling fan speed sensor.

These 5-volt reference circuits are independent of each other outside the PCM, but are bussed together inside the PCM. Therefore a circuit condition on one sensor 5-volt reference circuit may affect the other sensor 5-volt reference circuits. The PCM monitors the voltage on the 5-volt reference circuit. If the PCM detects that the voltage is out of tolerance, DTC P0641 sets.